By most accounts, Affleck is a very good director and a very shitty actor.

I hope he didn't ruin his own movie by putting himself in it.

I went into the movie expecting just this. However, after enjoying the movie thoroughly, I now think that maybe the only person in Hollywood that knows how to direct Ben Affleck is Ben Affleck. I had no respect for him at all as an actor until I saw this film. However, in this film, he did a fine job. Nothing that should single him out for acting award honors, but he didn't ruin it and that surprised the hell out of me.